There have been developed an ever-increasing number of safety devices for the purposes of protecting the lives of drivers and passengers of automotive vehicles by the provision of incessant monitoring, using electronic devices such as a radar system in both the forward and rearward directions of the vehicle for determining a vehicle interval distance and/or relative velocity. Such systems warn the driver when the vehicle is entering a risky area of possible collision or contact with another vehicle in front, or provides the driver with information on the state of an object approaching in the rear, such as when the driver wishes to change lanes.
As typically shown in FIG. 1, the general construction of this type of radar system to be provided on an automotive vehicle is such that there is provided a front monitor section adapted to generally monitor and detect another vehicle or an object B travelling in the same lane in front of the vehicle A in question, and a rear monitor section adapted to observe other vehicles or objects C and D travelling behind vehicle A on both adjacent lanes, the former being essentially required to have a monitoring range of approximately 100 meters in the front of the vehicle A, while the latter has a monitoring range of approximately 50 meters in the rear thereof. The front monitor system of this application is designed to detect a vehicle interval distance and relative velocity with respect to the object B in the front, from the detected data obtain an appropriate or safe interval distance required at the vehicle A's travelling speed at that given moment, and then compare this interval distance with an actual interval with the object B at the given moment. When such actual interval is found to be shorter than the required safety interval, a warning is presented to the driver of the vehicle A from time to time in accordance with the extent to which the actual interval is shorter than the safe vehicle interval. The rear monitor system is designed to detect interval distances and approaching velocities of the objects C and D in blind spot locations which may be partially out of view to the driver on the adjacent lanes as typically shown in FIG. 1, and indicate information on the approaching objects C and D to the driver so that he may properly judge when to change lanes, for instance, for the purpose of passing or the like. In this connection, it is essential to provide an appropriate indication of information relating to the vehicle interval and the attitude of approach so that the driver of the vehicle A can instantly determine what action to take in meeting the situation around his vehicle.